1. Field of the Invention
This invention relates to a novel oxide-type superconducting flat-shaped wire and a method of producing the flat-shaped wire, more particularly to an oxide-type superconducting flat wire having a composite cross-sectional structure composed of an oxide phase exhibiting a superconducting property and a metal phase, particularly having a very high critical current density.
The superconducting flat wire of this invention can be used as a coil for a rotor and stator of rotator, a coil for energy storage, a coil for a plasma vessel of nuclear fusion, a cable for power transmission and distribution, a coil for a transformer, a coil for a particle accelerator, a magnetic coil for MRI and NMR, a coil for an electron microscope, a magnetic coil for an atomic-absorption spectrometer, a coil for an rotor and stator of a motor for an electric car, automobile, elevator and escalator, and a magnetic coil for a linear motor car.
2. Description of Related Art
As a high-temperature superconducting material having a much higher superconducting transition temperature than that of prior art superconducting materials, a lanthanum-barium-copper oxide was discovered by Dr. J. G. Bednorz and Dr. K. A. Muller at the beginning of 1986, and then an yttrium--barium--copper oxide (hereinafter referred to as Y--Ba--C--O or YBaCuO), which has a transition temperature of about 90 K, was discovered by Dr. Chu of Houston University in U.S.A in the spring of 1987. Such discovery was made also in China and Japan at that time. These discoveries in succession are called the "revolution of superconductors". Nowadays, there are intensively made fundamental studies on the composition, crystal structure, properties and theory of superconducting materials, practical studies on methods of synthesizing the materials, on electronic or power electrical applications of the materials and further on research or development of new materials exhibiting superconducting transition at room temperature or at a higher temperature.
In these studies, research and development, a technique of shaping the high-temperature superconducting materials occupies a position as an elementary technique in power electrical applications such as a superconducting magnet. In prior art superconducting alloys or chemical compounds, it is known that the cross section of the shaped article is constituted by a composite phase of a superconducting phase and a metal phase. The metal phase functions as a supporter for a superconducting material while the material is being plastically worked in a long article and heat treated, as a strength-holding means during or after coiling of a superconducting wire, or as a stabilizer against the superconducting-to-normal transition in applying electric current to the article.
As regards the production of oxide-type superconducting wires, possibilities of materials as a wire-constituting metal phase (hereinafter referred to as a metal sheath), methods of plastically working to realize wire-shaped articles and tried methods of heat treating the wire-shaped articles have been reported by, for example, newspapers, Nihon-Keizai Shimbun dated Mar. 4, 1987 and Apr. 3, 1987 and "New Superconductors--State of Development and Applications Thereof", published Nikkei-McGraw-Hill on Jun. 15, 1987. These wire-shaped articles have a critical current density of only at most several hundred amperes per square centimenter.
As mentioned above, the oxide-type superconducting wires already developed have a critical current density of at least two figures lower than the current density industrially required. Furthermore, no structure of wires to raise the critical current density of the wires has yet been sufficiently known.